1. Field of the Invention
The present invention relates to a method of cutting a board-like workpiece, such as a plaster board or veneer board, etc., and a saw tool for practicing the method.
2. Disclosure of the Prior Art
In the past, various kinds of electric saws have been used for cutting a board material, such as a plaster board or veneer board. For example, when a rectangular through-hole is formed in a veneer board with an electric saw of Utility Model Japanese Patent Publication No. 1-26402 that gives a reciprocating orbital motion to a saw blade thereof, a starting through-hole having a diameter large enough to penetrate the saw blade through the veneer board is first drilled in the veneer board, and then the veneer board is cut with the saw blade penetrating through the veneer board. However, such a formation of the starting through-hole needs an excess of working time and also creates difficulty in producing an accurate cutting operation.
As shown in FIGS. 27A to 27C, Utility Model Japanese Patent Publication No. 58-26751 discloses a saw blade 30P having a unique blade shape that is used when a window-like hole is formed in a polystyrene board or an insulation fiber board without forming a starting through-hole in the board. The saw blade 30P comprises a saw tooth section 31P, a back 32P and an inclined knife edge 33P extending from the lower end of the saw tooth section 31P to the lower end of the back 32P. Since the polystyrene board or the insulation fiber board may include wooden chips or bits of down and otherwise is a soft board material from the viewpoint of cutting resistance, the saw blade 30P can readily penetrate through the soft board material by pressing the knife edge 33P of the saw blade 30P against the soft board material while reciprocating the saw blade 30P up and down. Subsequently, the soft board material is cut by the saw tooth section 31P to form the window-like hole therein.
However, because plaster board and veneer board is a harder material and has greater cutting resistance than soft board material, it is difficult to penetrate such a knife edge 33P through this material. Additionally, there is a probability of causing serious injury to the worker by a broken saw blade 30P in this case.
In addition, since the saw tooth section 31P is formed on one side of the saw blade 30P, only a one-way cutting operation is allowed. That is, in case of accurately forming a window-like hole in a board with the saw blade 30P without forming a starting hole in the board, the saw blade 30P is first caused to penetrate the board at an optional position of a cutting line on the board, and then the board is cut by advancing the saw blade 30P from the position to an end of the cutting line. Subsequently, the saw blade 30P is pulled out from the board, turned to the opposite direction, caused to penetrate the board again, and advanced from the position to the other end of the cutting line. In this case, although it is not necessary to form the starting hole in the board, the problem of requiring an excess of working time is not sufficiently improved.